Experimental Evidence of the Origin of Nanophase Separation in Low Hole-Doped Colossal Magnetoresistant Manganites

While being key to understanding their intriguing physical properties, the origin of nanophase separation in manganites and other strongly correlated materials is still unclear. Here, experimental evidence is offered for the origin of the controverted phase separation mechanism in the representative La1-xCaxMnO3 system. For low hole densities, direct evidence of Mn4+ holes localization around Ca2+ ions is experimentally provided by means of aberration-corrected scanning transmission electron microscopy combined with electron energy loss spectroscopy. These localized holes give rise to the segregated nanoclusters, within which double exchange hopping between Mn3+ and Mn4+ remains restricted, accounting for the insulating character of perovskites with low hole density. This localization is explained in terms of a simple model in which Mn4+ holes are bound to substitutional divalent Ca2+ ions.